1. Field of the Invention
This invention relates to a display element and a process for manufacturing the same. More particularly, it relates to a display element in which partition walls with which a display medium interposed between a pair of substrates is divided for each display pixel in the direction perpendicular to the substrate faces have been formed by a self-assembling material and a process for manufacturing the same.
2. Related Background Art
In recent years, with the advancement of information machinery, there has been an increasing demand for thin-type display elements with low power consumption. Research and development on display elements conformable to such demands is earnestly conducted. In particular, liquid crystal display elements can perform display by electrically controlling the arrangement of liquid crystal molecules to change optical characteristics of liquid crystal and have been developed and commercialized as display elements that can meet the above demand.
These liquid crystal display elements, however, have problems in that characters or letters displayed on a screen are viewed with difficulty depending on the angles at which a user watches the screen and on reflected light and in that there is a load on sight that is ascribable to the flickering of a light source or to low brightness. These problems have not been solved well. Accordingly, studies are energetically made on display elements having less load on sight.
As one such display element, an electrophoretic display element invented by Harold D. Lees et al. is known (U.S. Pat. No. 3,612,758). FIGS. 13A and 13B schematically illustrate the construction of the electrophoretic display element and its performance principle.
As shown in FIG. 13A, the electrophoretic display element has a pair of substrates 5a and 5b disposed leaving a stated space between them, and electrodes 5c an 5d are formed on the substrates 5a and 5b, respectively. Also, a large number of positively charged and colored electrophoretic particles 5e and a dispersion medium 5f colored in a color different from that of the electrophoretic particles are filled into the space between the substrates. Still also, partition walls 5g are so disposed as to divide the space into a large number of pixels arranged in the plane direction of the substrates and are so constructed that the electrophoretic particles can be prevented from localizing and also the space between the substrates can be defined.
In such a display element, as shown in FIG. 13A, a voltage with negative polarity is applied to the electrode 5c on the lower side as viewed in the drawing and also a voltage with positive polarity is applied to the electrode 5d on the upper side as viewed in the drawing, whereupon the electrophoretic particles 5e standing charged positively collect in such a way that they cover the electrode 5c on the lower side. When the display element is viewed from the direction shown by an arrow, display is performed in the same color as that of the dispersion medium 5f. On the contrary, as shown in FIG. 13B, a voltage with positive polarity is applied to the electrode 5c on the lower side as viewed in the drawing, and also a voltage with negative polarity is applied to the electrode 5d on the upper side as viewed in the drawing, whereupon the electrophoretic particles 5e collect in such a way that they cover the electrode 5d on the upper side. When the display element is viewed from the direction shown by an arrow, display is performed in the same color as that of the electrophoretic particles 5e. Such drive is performed for each pixel, whereby any desired image is displayed by a large number of pixels.
Meanwhile, as a self-luminescent display element, an organic EL(electroluminescence) element proposed by C. W. Tang et al. is known (Appl. Phys. Lett., vol. 51, p.913 (1987)).
FIG. 14 schematically illustrates a conventional organic EL display element. As shown in FIG. 14, the display element has a pair of substrates 6a and 6b disposed leaving a stated space between them. The substrate 6a is a transparent glass sheet or the like. On the substrate 6a, a first electrode 6c formed of a transparent electrode of ITO (indium-tin oxide) or the like is provided. On the substrate 6a including the first electrode 6c, partition walls 6e having electrical insulation properties are arranged and formed at given intervals. On the first electrode 6c at which partition walls 6e are not formed, at least one layer of thin film of an organic EL medium 6f is formed. Second electrodes 6d are further formed on the organic EL mediums 6f. The face side where the partition walls 6e and the organic EL medium 6f are formed is covered with a substrate 6b, and the edge space between the substrates 6a and 6b is sealed with an adhesive 6g.
In the organic EL display element, electric fields are applied across the first electrode 6c and the second electrodes 6d, where the organic EL mediums 6f emit light to perform display through the substrate 6a. 
Conventional electrophoretic display elements have had a problem as stated below. In order to perform more highly minute display, the electrode pattern must be made more highly minute, and correspondingly thereto the partition walls also must be minutely provided. However, to form partition walls minutely on the substrate by conventional lithography, a large number of steps are required, and the partition walls can not be formed simply.
Conventional organic EL display elements also have had a problem as stated below. In order to perform more highly minute display, pixels must be made smaller, and correspondingly thereto the partition walls also must be minutely provided. However, to form partition walls minutely on the substrate by conventional lithography, a large number of steps are required, and the partition walls can not be formed simply.
The present invention was made in order to solve the problems stated above. Accordingly, an object of the present invention is to provide a display element having partition walls which can be simply formed without relying on any conventional lithographic techniques.
Another object of the present invention is to provide a display element in which the partition walls with which a display medium interposed between a pair of substrates is divided in the direction perpendicular to the substrate faces are formed simply by self-assembly of a self-assembling material to enable highly minute display.
The present invention is to provide a display element comprising a pair of substrates, a display medium interposed between the substrates, and partition walls with which the display medium is divided in the direction perpendicular to the substrate faces, the display medium being provided in hollows defined by the partition walls and the substrates and the partition walls being formed of a self-assembling material.
The self-assembling material is herein meant to be a material that can form a structural body by spontaneous association of molecules of the material when a solution of the material is cast on a substrate at high atmospheric humidity. Its details are given later.
As a feature of the present invention, the display element may have structure in which the hollows defined by the partition walls and the substrates are arranged in a honeycomb fashion, and the hollows may each have a hollow diameter of from 10 xcexcm to 200 xcexcm and a partition wall height within the range of from 0.1 xcexcm to 100 xcexcm, having an aspect ratio within the range of from 0.1 to 100, and may be arranged at intervals between hollows of from 10 xcexcm to 210 xcexcm.
The self-assembling material may also comprise a block copolymer, a homopolymer, a polyion complex or an organic and/or inorganic hybrid material.
The partition walls may also have a conductivity or may be in a structural body formed by self-assembly of a conductive polymer.
The present invention is also a process for manufacturing a display element comprising a pair of substrates, a display medium interposed between the substrates, and partition walls with which the display medium is divided in the direction perpendicular to the substrate faces, the process comprising the steps of:
(1) forming the partition walls on one substrate by self-assembly of a self-assembling material;
(2) filling a display medium into hollows defined by the partition walls and the substrates; and
(3) covering the display medium and the tops of the partition walls with the other opposing substrate, and sealing the edge space between the substrates.